1. Field of the Invention
This invention relates to chemical synthesis and, more particularly, to chemical synthesis involving chalcogens.
2. Art Background
The use of Se and S in organic and inorganic chemistry has been investigated for many years. However, interest has intensified particularly in organic Se and S chemistry since various heterocyclic compounds containing these elements have shown unusual properties such as high electronic conductivity useful for a variety of applications such as the production of high field magnets. For example, the discovery that tetramethyl tetraselenafulvalene is a superconductor at temperatures of approximately 0.9 degrees K. and pressures of approximately 12 Kbar has generated a great deal of excitement.
The synthesis of chalcogen, and particularly of Se containing compounds such as tetramethyl tetraselenafulvalene, however, often relies on the reactions of extremely undesirable materials such as carbon diselenide. Unfortunately, this reagent is both necessary for producing C.dbd.Se bonds (through the production of dichalcogen carbamate), and also particularly inappropriate for most commercial synthetic processes. Carbon diselenide, in fact, has several disadvantageous properties. For example, its odor is among the most noxious of all commonly used reagents. This undesirable property is compounded by its high density that makes typical fumehoods ineffective for removing its vapors from the atmosphere. This problem discourages its use in industry for synthetic processes. Additionally, its odor makes commercial synthesis unacceptable to the communities where production plants might be located.
Even if carbon diselenide were odorless, it would not be particularly suitable for large scale production and distribution. Carbon diselenide is usually produced by reaction of methylene chloride with Se at elevated temperatures. This reaction produces carbon diselenide in quite limited yields and further produces a host of other noxious chemicals. Thus, its production is expensive and presents additional toxicity problems. Further, carbon diselenide has a tendency to decompose and, therefore, does not transport or store well.
As a result of these problems the use of carbon diselenide has been limited to laboratory preparation where it is feasible to produce the reagent in situ and where environmental considerations are not as significant. These restrictions have limited the preparation of useful inorgano and organo selenium compounds and, in particular, has limited the preparation of Se heterocyclic compounds.